Semen Sexing

SEXED SEMEN IS NOW A REALITY FOR CATTLE BREEDERS by: Heather Smith Thomas

Use of sexed semen is now a reality for many cattle breeders. The early research on this technology was done by USDA more than 15 years ago. The first sex-selected calf using frozen sexed semen and AI was born in 1999. In 2004 this process became commercially available through a company called Sexing Technologies with labs in Texas, Ohio, Wisconsin and Brazil. Gustavo Toro, Marketing Director for GRI (Genetic Resources International) and sister company Sexing Technologies, says that the research was done by Dr. Larry Johnson from Colorado State University, in conjunction with a grant from the USDA. Johnson developed a method for staining sperm, to facilitate sorting, and worked closely with Mike Evans (Sexing Technologies) to develop the instruments needed. "When the technology was developed and a patent issued, a company called XY Inc. of Fort Collins, Colorado, bought the patent. Our company, Sexing Technologies, has a license for the U.S. and a few other countries. We are the largest company dealing with sexed semen. Our headquarters in Navasota, Texas is where we do all the research and training. We also produce sexed semen for individual customers as well as the big AI centers," says Toro. "We have a second lab in Brazil. In March, 2006 we opened a lab in Ohio with Select Sires. In August of 2006 we opened a lab with ABS in Wisconsin. In May 2007 we opened one in Holland. We've also signed a contract with Genex and AltaGenetics and we have their bulls here in Texas where we are collecting for them. So we are now lined up with the five biggest AI studs in the world. We have our labs and machines in their facilities," says Toro. In Texas some of the private customers include producers of rodeo stock, like Vernon Guidry and Bucks by Design. "We have done several of the bucking bulls, and I think this will become a very important tool in that industry. It is growing rapidly," he says. Use of sexed semen in the beef industry is also starting to catch on. The dairy industry is using this technology the most, however, because almost all of those breeders utilize AI. Only six percent of the beef cows in this country are bred by AI, compared with almost 90 percent in the dairy world, says Toro. "We have now done sexed semen for 18 different breeds. Interest is increasing daily. We thought we would just have four machines in Texas, but we have nine running at present and will soon have 11. Select Sires started with four and now they have eight. ABS started with four and we are now installing four more for them; they can't keep up with demand," says Toro.

The bulls have to be at one of these studs in order to have this process done. "The only facility where we are doing custom work for people is here in Texas. All of the others are just processing their own bulls. They are not offering this service to any outside bulls," he explains. COST -- The cost of processing sexed semen is about $35 to $60 per straw, depending on the quantity being done. Dr. Bob Everett at Cornell University did a study to show the economic return to producers using sexed semen. In several instances, having a calf of the desired sex from a certain cow/bull combination will more than pay for the cost, and may even return several hundred dollars on that investment. THE TECHNOLOGY -- "The way the process is done is based on the fact that the x chromosome has 3.8 percent more DNA than the y. The machines can read that difference in DNA content," says Toro. The semen is stained with a fluorescent dye and then passed through a machine (flow cytometer) that can sort the sperm as it goes by in a stream of single droplets. The female producing sperm with the x chromosome shines brighter than the y because the x chromosomes are 3.8 percent larger and have absorbed more dye. A laser in the sorting machine determines the gender of the sperm based on the amount of light it emits. In developing this technology, Dr. Johnson modified existing flow cytometers to accomodate analysis of stained sperm. Flow cytometry is the measurement of cells as they flow by a detector. The flow cytometer uses focused laser light to illuminate cells as they pass by the laser beam one at a time in a fluid stream, traveling 60 miles per hour; more than 4000 sperm per second are sorted and processed. This seems fast, but it takes about three to four times longer to process sexed semen than to process conventional semen for shipping or freezing. The X-bearing sperm are sorted off in one direction, the Y- bearing sperm in another, and anything of undetermined sex passes straight through as waste. The sorted sperm are then frozen in .25 cc straws to be used for AI. An ejaculate yields fewer straws of sexed semen than conventional semen. One advantage to the sorting process (which also helps make the sexed semen more successful in low dosage than regular sperm) is that damaged or dead sperm are sorted off. A normal ejaculate always has a certain amount of dead, dying or damaged sperm cells, so when it's sorted by the sexing process, these are eliminated -- making the remaining sperm more viable. The highly purified groups of sorted semen are then frozen for future use in AI, to enhance AI programs or embryo transfer. For many years the drawback in using sexed semen was the difficulty in getting enough sorted sperm from an ejaculate to make it practical. Studies at Colorado State University helped make it feasible. Their theory was that since it only takes one sperm to fertilize an egg, why use 20 million (the recommended amount for optimum reproduction)? They began experimenting with low

dose insemination for AI, and it worked -- especially if the cow was at the optimum point in her heat period. Today, advanced reproductive techniques like in vitro fertilization (where the egg is fertilized in the lab and then used in embryo transfer) make sexed semen even more practical, since only a tiny amount of sperm is needed for fertilizing a large number of eggs. Sexed semen works well (with highest success rates) in a well managed AI or ET program in which timing of insemination is optimum for proper fertilization of the egg, but probably works best in an IVF program. Some variability has also been noted with different bulls; semen from various bulls goes through the sorting machines differently, so some bulls are better candidates for sexed semen than others. BENEFITS OF USING SEXED SEMEN -- When using sexed semen, the results are predictable about 93 percent of the time. It can be a handy tool to increase your heifer numbers or steer numbers. This option is very useful for the dairy industry, since there is always a market for heifer calves but not for the bull calves. In the beef industry, it is handy to be able to select the gender of calves if the producer wants to keep replacement females from certain cows/bulls, or wants just steers from a terminal cross. In any given herd, the option of sex determination could be useful for reducing calving difficulty in first calvers (since heifer calves are typically smaller at birth than bull calves), or for producing a higher number of good females to choose from as replacements if you are wanting to expand your herd size without buying outside cattle. If you can keep a closed herd, not having to depend on bringing in any other females, you can cut down on some of the health problems that may be inadvertantly introduced, and in many cases you also have better knowledge of the genetics in your own herd. If you want your best cows to all have heifers, this can give you faster genetic progress in improving your cow herd, enabling you to keep more good females and cull more deeply. "A producer may want heifers from the top 10 to 15 percent of their cows, and steers from the rest of the herd," says Toro. When the market is good for replacement females, breeders may opt for more heifers, and when the market is better for steers they may choose to produce mostly male calves. Seedstock producers may have bloodlines they are selecting for maternal qualities for brood cows and others they are hoping to use for marketing bulls. This technology gives producers the choice, and also enables them to develop an early strategy for a potential future market. In female sales, for instance, some breeders are finding their bred cows and heifers worth more when bred with sexed semen. Bred heifers guaranteed to have heifer calves (and less calving problems) may bring a premium. Other buyers may want females that will produce only male calves. Seedstock producers marketing pen lots of bred females or pairs may find an advantage in being able to offer cattle guaranteed to have one sex or the other, or may find a premium in offering exceptional female bloodlines in a 3-way package -- a cow with heifer calf at side and bred back to have another good heifer calf.

For more information on sexed semen, contact GRI or Sexing Technologies at 936-8703960 or [email protected] or visit their website at www. griglobal.com